Traditionally, advanced electronic display systems have only been used for indoor applications or outdoor applications where the variation in temperature and/or amount of direct sunlight is limited. When these systems are moved outside and/or into direct sunlight, both elements become significant factors in the display's ability to accurately create a viewable image.
Bright ambient environments and/or direct sunlight can limit the visibility of the display, as the reflection of the ambient light rays off a display surface may be brighter than the light which is generated by the display. Past devices have attempted to account for indoor ambient light levels and adjust the display accordingly but these devices have not performed adequately (especially when used in direct sunlight). When used in outdoor and/or direct sunlight environments, the issue of ambient light and the adjustments for ambient light become even more important. Not only is an adjustable system important for optimizing the image produced by the display, but energy consumption by large, bright displays has also become a major concern. It is now desirable to limit the energy consumption of electronic displays by dimming them when the ambient conditions are very dark and using the brightest (most energy-draining) settings only when the ambient light is very high. It is desirable not only to meet these minimum and maximum settings, but also adjust for all ambient light levels in between.
LCDs typically contain a liquid crystal stack which typically comprises several layers including two transparent plates which sandwich liquid crystal material in-between, front and rear polarizers, and an electrically conductive layer. The liquid crystal stack is usually semi-transparent and requires a backlight in order to properly filter the light and create an image. The power levels sent to the backlight can be measured by a circuit in an attempt to determine the illumination level of the backlight. However, for several reasons, it has been found that the actual illumination of the backlight does not always correlate with the power level being sent to the backlight. Thus, light sensors have typically been placed within the backlight in order to measure its level of luminance. However, when used in outdoor environments, the ambient light (sometimes sunlight but can also be headlights, streetlamps, signs, reflections of any of these, or other sources of ambient light) can sometimes penetrate the liquid crystal stack and interfere with the light sensor placed in the backlight assembly.
Thus, there is a need for a system and method to calibrate the backlights for electronic displays that may be subjected to a wide range of ambient light levels.